1. Field of the Invention
The present invention relates to an Internet Protocol (IP) telephone system using an IP network.
2. Description of the Related Art
A system for communicating voice information by using a best-effort type communication network, such as an IP network, has been widely introduced. Such a type of system is called an IP telephone system or a voice over Internet protocol (VoIP), and the system has firstly been used for an extension telephone system in an office, and it has begun to be applied to a wide area telephone network as well.
As for a terminal to be used for the IP telephone system (hereinafter, referred to as IP telephone set), there exists a personal computer (so-called soft phone) with software installed therein, and a telephone set developed specially for the IP telephone system. In recent years, a technique, by which a telephone set is provided with a rewritable memory, and a system program is downloaded in the memory to change or update the function of the telephone set, has been proposed (for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-72532).
As to one method for rewriting the software in the memory of the telephone set, directly transferring data for update to the telephone set from a server, and immediately updating the software at the IP telephone set on a reception side is a possible method. However, takes a fixed time to update the software, and it results in stoppage of a telephone service. Therefore, a conflict between timing at which a user expects to use the IP telephone set and timing at which the software to be updated poses such a problem that the user temporarily becomes to be disabled to enjoy the telephone service.